ITCT 2002
Intercontinental Transport and Chemical Transformation 2002


The NOAA P3 landing in Monterey. Note that the Georgia Tech Pod has the large yellow jacket on the nose cone.

The ITCT 2k2 field study investigated springtime transport and the composition of air masses along the Pacific coast of North America and attempted to identify the sources of the ozone and aerosols that are being transported into the atmosphere over the Western United States. One aim was to characterize the anthropogenic influence from the various continents on the ozone and aerosol budgets in this region. Greg Huey and Dave Tanner were the principal investigators of the hydroxyl radical (OH) and sulfuric acid (H2SO4) during this study in Monterey, California. Measurements were taken using the CIMS instrument that was mounted in an ALQ-170 electronics warfare p that is mounted underneath the wing of the NOAA P3.

Instrumentation layout of the NOAA P3 for the ITCT 2002 field mission.



Closeup of the Georgia Tech CIMS Pod



Picture of the Georgia Tech Mass Spectrometer with the nose cone of the pod removed.



Picture of forward electronics bay with access door removed.

Other Pictures




Results and Accomplishments

The primary goals of this work have been met. The Georgia Tech pod instrument was used to measure OH and H2SO4 from the NOAA P3 during ITCT 2002. The instrument can run unattended and can be monitored via a laptop computer mounted in the aircraft cabin. Data has been obtained on eight science flights and some preliminary observations can be reported. In general, very low OH and H2SO4 number densities have been observed on the flights that focused on high altitude transport of Asian pollution. Several air parcels have been encountered with enhanced CO, NOy, PAN, particulates, and acetonitrile levels. However, the OH and H2SO4 levels were very low and near the detection limit of the instrument of ~ 2 x 105 molec. cm-3. This results are consistent with the observed low dew points (TD < -30 oC) and small NOx and HNO3 levels (< 10 pptv) in these plumes. Soluble gases such as HNO3 and H2SO4 have been removed by cloud processing and uptake by particles during the ~ week long transit time from Asia. OH levels are probably low due to a lack of production via reaction (1) because of low water vapor and a large HO2/OH ratio at the observed NOx values. These observations will of course need to be confirmed by photochemical modeling.
More interesting data has been obtained during the flights that have concentrated on the effects of ship plumes and transport into and out of West Coast metropolitan areas. The flight track for such a flight on May 8, 2002 is shown in the following figure.

The first four hours of the flight were used to investigate ship plumes in the marine boundary layer and the last half explored San Francisco, Oakland and the Central Valley. Time series of H2SO4 and NOy data are plotted in the figure below.



The coincident sharp spikes in both measurements correspond to transects of ship emission plumes. The sharp spikes are overlaid on a broad background of relatively high levels (~ 5 x 106 molec. cm-3) of H2SO4 in the marine boundary layer. This background level is much higher than in other portions of the marine boundary layer sampled on this mission and is approximately equal to the background levels in San Francisco. These data along with elevated ozone, particulate sulfate and NOy values definitely indicate that ship emissions are significantly perturbing the atmospheric chemistry of large portions of the marine boundary layer.

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